Human Horn is actually a ground up powder made from human noses, which are mistakenly believed to be the human reproductive organ by some alien races. As such, it is a sought-after aphrodisiac, although any effects it may have are purely placebo in nature.
Aliens eventually stopped trading in Human Horn after they learned the truth about it, although some alien species still seek the, uh, lower human horn for the same purposes.
Related Drugs: Comatonin, Dr Flim Flam’s Miracle Cream, Electricity, Slurm & Space Honey